The present invention relates to a threaded tubular connection which is leakproof under static loads such as axial tension, axial compression, planar bending, internal or external pressure and combinations thereof.
Such leak-proof threaded tubular connections, hereinafter termed connections, may be obtained by assembling a male element at the end of a first tubular component which may, for example, be a great length tube and a female element at the end of a second tubular component which may, for example, be a great length tube or a coupling, each of said elements being provided with a metallic sealing surface and being radially interference fitted against the metallic sealing surface of the other element.
Said connections are in particular used to produce leak-proof casing strings or tubing strings for hydrocarbon wells or for similar wells such as geothermal wells.
The metallic sealing surfaces (or metal-metal sealing surfaces) of the male and female elements of such connections are extremely critical zones which produce the sealing characteristics of the connection.
In hydrocarbon wells, such connections are subjected to various loads such as tension, compression, bending along the tube axis, or pressure. Those various loads may vary with time, for example when cementing casing strings (increase of external pressure) or during production (increase in internal pressure) or also during maintenance operations (production stop then start-up) and they may act alone or in combination.
Such connections are expected not only to tolerate such mechanical loads but also to remain leak-proof when they are applied.
For this reason, the present invention seeks to improve such connections in order to increase their sealing characteristics, in particular to optimize the function of the metallic sealing surfaces.
The prior art for such connections proposes means for improving the sealing characteristics of metal-metal sealing surfaces which are subjected to a wide variety of static loads, which have in particular been described in French patent FR 2 359 353 and International patent application WO 2006/061577.
FR 2 359 353 discloses a connection which is tight to differential pressures, comprising a male element having a male threading, a female element with a complementary female threading, an outer abutment comprising a tapered annular surface located on the male element and a corresponding frontal surface located on the free end of the female element, and an outer metal-metal seal comprising a first metallic sealing surface disposed on the female element and a second metallic sealing surface disposed on the male element.
When that connection is subjected to an external differential pressure, i.e. an external overpressure, the metallic sealing surfaces are applied against each other even more strongly and the connection is thus self pressurizing. In the case of an internal differential pressure, i.e. an internal overpressure, the annular and frontal outer abutment surfaces are applied more strongly against each other.
International patent application WO 2006/061577 describes a connection provided with an outer metal-metal seal subjected to tension and compression loads. Such a threaded connection includes a female element comprising an abutment, a threading and an annular groove located between said abutment and said threading. Said annular groove, which is rectangular in shape and relatively short, enables to facilitate machining of full height threads on the female element because the thread-producing tool can be withdrawn more easily, to obtain a connection which is stronger in tension because of the longer thread length and to concentrate loads over a small zone at the groove rather than at the abutment. Said load concentration over a small zone at the groove enables, according to that document, to localize a maximum amount of load at that level without plastifying the abutment.
However, the sealing performance of such prior art connections which are successively subjected to internal and external pressure loads has not been considered.
In particular the inventors have observed that connections such as those described in FR 2 359 353 have reduced leak-proofing performance when subjected in succession to the application of internal pressure then external pressure.